The invention relates to polymer coated paperboard products, and more particularly to dual ovenable paperboard products.
Many food items are precooked and frozen for long term storage before cooking. In the past foods were often packaged in aluminum cooking trays. Such containers have become less popular with the increasing popularity of microwave ovens since metal containers cannot normally be used for microwave cooking. There is now a desire in the industry to package frozen and prepare foods in containers which are dual ovenable, that is able to be used in both microwave and conventional ovens.
Paperboard-based containers have thus become widely used as containers for prepared foods. Such materials offer the advantages of being microwavable as well as suited for use in conventional ovens. In some instances, however, plain paperboard is not able to be exposed to temperatures typically encountered during cooking. Certain polymer based coatings have been developed for application to paperboard to reduce the charrability of the container.
One commonly used coating is a polyester material. This contributes moderate heat stability to the paperboard so that it is able to resist charring up to about 400.degree. F.(203.degree. C.). One disadvantage of this material is that it can be difficult to recycle and thus may raise environmental concerns. Further, the use of polyester coatings is relatively expensive and does not afford ideal heat stability as paperboard coated with polyester can warp during heating.
U.S. Pat. No. 4,421,825 discloses a paperboard product coated with a first layer which includes titanium dioxide, a second layer of an acrylic copolymer and an organic solvent, and one or more outer layers comprising a clear acrylic copolymer also dissolved in an organic solvent. Paperboard to which such coatings have been applied are reported to be able to resist charring at temperatures up to 205.degree. C. (approximately 400.degree. F.). However, the coating process can present environmental problems because the organic solvent is volatized during the drying process. The use of a titanium dioxide pigment in the first coating can also reduce the aesthetics of the resulting food as the pigmented coating tends to be brittle and staining can result in areas where the container has been folded or scored.
It would thus be advantageous to provide coated paperboard products which have high temperature stability and which offer ease of manufacture.
Accordingly, it is an object of the invention to provide a dual ovenable food container manufactured from a paperboard substrate. A further object is to provide a paperboard food container coated with one or more aqueous based polymer emulsions which enable the paperboard product to be used effectively at temperatures in the range of 450.degree. to 500.degree. F. (232.degree. C. to 260.degree. C.). Another object of the invention is to provide a polymer coated paperboard product, the manufacture of which can minimize environmental dangers. Other objects of the invention will be apparent upon reading the following description.